Premixing tetanus toxin with the monoclonal antibody, 18.2.12.6, results in a two- to three-fold increase in the amounts of toxin and antibody bound to the neuronal surface when the formed complex is applied to neuronal cell cultures, relative to what is bound when the reagents are added sequentially. The binding portion of the toxin molecule, Fragment C, can be substituted for the intact toxin, providing a non-toxic complex that can be used to label the surface of living neurons. The complex persists on the cell surface for several days, and can be used to identify neurons shortly after plating and to study morphological aspects of early development.